1. Field of the Invention
The present invention relates to a phase detecting module and phase detecting method thereof, and more particularly, to a phase detecting module capable of avoiding noise influence and a phase detecting method thereof.
2. Description of the Prior Art
Many signal processing circuits, e.g., phase locked loops (PLLs), usually comprise phase detectors each implemented for determining a phase relationship between two signals, and transmit the comparing result generated from the phase detector to other signal processing units for further processing.
FIG. 1 is a block diagram illustrating a PLL 100 according to the prior art. As shown in FIG. 1, the conventional PLL 100 usually includes a phase detector 101, a charge pump 103, a low pass filter (LPF) 105, a voltage-controlled oscillator (VCO) 107, and a plurality of frequency dividers 109 and 111. The frequency divider 111 is for frequency-dividing an input signal IS which has an input frequency Fin to form a reference signal RS which has a reference frequency Fr. The phase detector 101 is for comparing the reference signal RS with an output signal OUS which has an output frequency Fou to generate a phase detecting signal DS. The charge pump 103 determines to increase or decrease outputted charges according to the phase detecting signal DS which could be an up signal or a down signal. The voltage outputted by the charge pump 103 is processed via the LPF 105 to form a filtered control voltage VCF, and the VCO 107 thereby determines the outputted oscillation signal OS which has an oscillation frequency Fo according to the control signal VCF. The frequency divider 109 frequency-divides the oscillation signal OS to form the output signal OUS. As other detailed architecture and operations should be readily comprehended by those skilled in the art, further description is omitted for succinctness.
From the aforementioned description, the charge pump 103 primarily operates to raise or lower a following voltage according to the phase detecting result generated from the phase detector 101. However, when the phase difference between two signals is very small, the phase detector 101 will not be able to determine the phase relationship between the two signals due to the noise or jitter attached onto the two signals, leading to a problem in the following signal processing.